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Öğe Effect of doping by low content of yttrium at Ca and Sr sites of Bi(Pb)-2212 superconducting ceramics(Elsevier, 2011) Amira, Abderrezak; Boudjadja, Y.; Saoudel, A.; Varilci, Ahmet; Akdoğan, Mustafa; Terzioğlu, CabirIn this work, a comparative study of the effect of doping bylaw content of Y3+ between (Ca site) and out of (Sr site) the CuO2 planes of Bi(Pb)-2212 phase is presented. Ceramics of Bi1.6Pb0.4Sr2Ca1-xYxCu2O8+d (called CY series) and Bi1.6Pb0.4Sr2-xYxCaCu2O8+d (called SY series) with x=0, 0.025, 0.05, 0.075 and 0.1 are elaborated in air by conventional solid state reaction. They are characterized by X-ray diffraction (XRD), Scanning Electronic Microscopy (SEM), density, Vickers microhardness and resistivity measurements. The refinement of cell parameters is done by considering the structural modulation. In comparison with the undoped sample (x=0), the cell parameters a, b and c are reduced by the doping for both series while the b component of the modulation vector increases. A good correlation between the variations of the bulk density and the Vickers microhardness with x is obtained. For both series, the SEM analysis shows that the doped samples exhibit a reduced grain size than that of the undoped one. The variation of resistivity with temperature shows that all samples exhibit a metallic-like character in the normal state. For all doping levels, the CY series presents higher onset critical transition temperature than that of the undoped sample, which is equal to 85.43 K. The opposite is obtained for SY series. The highest value of this temperature is obtained for x=0.075 in the doped samples and is about 92.15 and 79.96 K for CY and SY series, respectively. These values may correspond to a near optimally doped state since the slope (d rho/dT) of resistivity shows a maximum at the same value of x=0.075. For both series, when Y3+ is introduced into the samples, the residual resistivity decreases first for x=0.025 and increases gradually after this value until x=0.1. (C) 2010 Elsevier B.V. All rights reserved.Öğe Effect of fluorine doping on phase formation and properties of Bi(Pb)-2223 ceramics(Elsevier Science Bv, 2011) Amira, A.; Saoudel, A.; Boudjadja, Y.; Amirouche, L.; Mahamdioua, N.; Varilci, Ahmet; Akdoğan, Mustafa; Terzioğlu, CabirSuperconducting ceramics of Bi1.6Pb0.4Sr2Ca2Cu3OyFx (x = 0-0.6) are prepared in air by conventional solid state reaction and characterized. The study shows that the melting point of the samples decreases as fluorine content increases. As a consequence, the grain size increases with the doping level and for x = 0.6, the sample is completely deformed and presents a concave shape making impossible the measurements on it. The Vickers microhardness reaches its maximum for x = 0.2. The analysis of the X-ray diffraction results reveals that all the samples are composed of only Bi(Pb)-2212 and Bi(Pb)-2223 phases. The highest proportion of the high T-c phase (Bi(Pb)-2223) is also observed for x = 0.2 and is about 67.32%. The refinement of cell parameters is done by considering the structural modulation. The results show that the doping leads to a reduction of cell volume as well as the a axis component of modulation. Fran resistivity versus temperature measurements, it is shown that the doped phases exhibit higher onset critical transition temperatures than the undoped one. The residual resistivity increases with fluorine content suggesting that the doping introduces structural defects and disorder into the samples. The obtainal critical current density at 77 K under zero magnetic field also increases with fluorine doping. (C) 2011 Elsevier B.V. All rights reserved.Öğe Effects of thallium fluoride and yttrium on structure, electrical properties and ac losses susceptibility of (Bi,Pb)-2234 superconductors(Elseiver Science Ltd, 2021) Saoudel, A.; Saoudel, Assia; Boudjadja, Y.; Bouchekhou, H.; Allag, H.; Altıntaş, Sevgi PolatWe have studied the effects of thallium fluoride TlF3 and yttrium Y3+ on phase formation and superconducting transport properties of Bi1.8_xTlxPb0.35Sr2Ca3_ zYzCu4O12+delta F3x superconductors. The samples are characterized by X-ray diffraction, SEM photographs, resistivity and AC susceptibility chi '(chi '') measurements. The study showed that the melting point of the sample doped with thallium fluorine and yttrium as well as the formation temperature is decreased. We have found that the agreement factors of structure (Rp,Rwp,GOF) and the superconducting parameters as the transition width, the activation energy, the residual and normal resistivity were enhanced with TlF3 and Y3+ doping. This behavior attests of the improvement of flux pinning strength into the grains and their coupling matrix. The inter-granular AC loss peak temperature was observed to increase as doping which is mainly due to a strong links between the grains. However, it is widely decreased with magnetic field. The maximum of susceptibility (chi''max) and partial susceptibility of matrix (chi ''m,max), and the effective volume fraction of the grains (fg) are determined on the basis of the critical state model which proved a great improvement with doping under applied field of 2 and 10 Oe. The estimated values of matrix susceptibility through this model revealed the well decrease of the inter-granular losses with doping as well.Öğe Microstructural and magneto-transport properties of Bi1.6Pb0.4Sr2Ca1-xGdxCu2O8+delta superconducting ceramics(Elsevier, 2017) Boudjadja, Yazid; Amira, Abderrezak; Mahamdioua, Nabil; Saoudel, A.; Menassel, S.; Varilci, Ahmet; Terzioglu, Cabir; Altıntaş, Sevgi PolatThis study aims to investigate the effect of Gd doping on the phase formation, microstructure, transport and magnetic properties of the Bi(Pb)-2212 system. A series of superconducting bulks with a nominal composition of Bi1.6Pb0.4Sr2Ca1-xGdxCu2O8+delta with x= 0, 0.05, 0.10 and 0.15 are synthesized by the solid state synthesis route. The formed samples are characterized by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), electrical transport and magnetic measurements. The experiment results reveal that all the samples doped are composed of Bi-2212 phase and traces of Bi-2201 secondary phase when compared to the undoped sample. The refinement of cell parameters shows that the doping reduces the cell volume of the samples. The texture degree decreases with doping while the degree of orthorhombicity increases. Quantitative EDS analysis confirms that Gd atoms are successfully introduced into crystalline structure. The SEM micrographs show randomly distributed grains with a flake-like shape. The highest value of onset critical transition temperatures is obtained for x= 0.10 and is about 90.22 K, which correlates well with the observed slope of resistivity and the hole concentration of the CuO2 layers. Magnetic hysteresis loops suggest that the diamagnetism, remanant magnetization and lower critical field are better for x= 0.10. Based on the enhancements of both grain boundary weak-links and flux pinning centers, improvement of the critical current densities and flux pinning density is obtained with this kind of doping.Öğe Structural and magneto-transport properties of copper doped double layered manganites La1.4Ca1.6Mn2O7(Springer, 2013) Mahamdioua, Nabil; Amira, Abderrezak; Altıntaş, Serpil Polat; Saoudel, A.; Boudjadja, Yazid; Varilci, Ahmet; Terzioğlu, CabirSamples of La1.4Ca1.6Mn2-xCuxO7 with 0 <= x <= 0.075 were prepared by a solid state reaction and characterized. The cell parameters and volume increase with increasing doped content in all the samples. The metal-insulator (MI) transition was observed in all the samples except for x = 0.075. The doping increases the MI transition temperature and resistivity. The application of a magnetic field increases the transition temperature. It can be referred to the suppression of the ferromagnetic-insulator state around it. The magnetoresistance (MR) of the undoped and 0.025 Cu-doped samples is observed on a wide range of temperatures (3.5-283 K). The undoped one exhibits a maximum value of 39.7 % at 5.07 K under 5 T. The 0.025 Cu-doped one exhibits a maximum value of 40.65 % at 44 K in the same magnetic field. No MR effect is shown for the 0.05 doped sample. The 0.075 doped sample exhibits a small negative MR behavior and a second peak of resistivity at a very low temperature.
